Nondisintegrating alloy



Unite rates 3,032,412 NONDISINTEGRATHNG ALLOY Robert W. Freeman, St.Catherines, Ontario, Canada, as-

signor to Union Carbide Corporation, a corporation of New York NoDrawing. Filed Apr. 8, 1960, Ser. No. 2%),340 4 Claims. (Cl. 75-438)This invention relates to an addition agent for refining aluminum alloysand, in particular, to a phosphorusbearing silicon-base addition agent.

It is common practice in the aluminum industry to use small amounts ofvarious addition agents for the purpose of improving the structure ofaluminum alloy castings. Heavy-sectioned castings show a markedimprovement in properties as a result of the finer grain structureafforded by the use of modifiers for example.

Another suggested procedure involves the addition of phosphorus which isknown to function effectively in hypereutectic aluminum-silicon alloysas a nucleating agent for refinement of the primary silicon phase duringthe precipitation of this phase.

A commercially acceptable means for providing for an addition ofphosphorus is needed, however. Alloy addition agents consisting ofphosphorus and copper are used but are not always suitable because thecopper addition is sometimes detrimental to the finished casting.Addition agents composed of phosphorus and silicon, a seemingly usefulcombination for use with-aluminum-silicon alloys, have been suggestedbut have heretofore been unacceptable for general foundry use because ofthe tendency of a silicon-phosphorus alloy to disintegrate duringstorage.

The disintegration of such silicon-phosphorus alloys is not due to themere crumbling of a brittle material, but rather is a spontaneouscrumbling or disintegration of a previously sound silicon-phosphorusalloy upon standing. The tendency to disintegrate is accelerated byexcessive moisture conditions.

The disintegration of these silicon-phosphorus alloys is detrimental inthat such materials are not suitable for use in present-day foundrypractice; and also because the disintegration of the alloy liberatespotentially dangerous phosphine gas.

It is the primary object of this invention, therefore, to provide anondisintegrating silicon-phosphorus alloy.

It is also the object of this invention to provide a stable,nondisintegrating silicon-phosphorus alloy for use as a refining agentfor alumnium alloys.

Other aims and advantages of this invention will be apparent from thefollowing description and the appended claims.

In accordance with these objects a silicon-phosphorus alloy is providedconsisting essentially of a maximum of 1 percent by weight phosphorus,less than 0.1 percent by weight aluminum, and the balance substantiallyall silicon and incidental impurities.

The alloy should preferably contain less than 0.13 percent by weight inthe aggregate of aluminum and calcium even when the aluminum content isless than 0.1 percent. Furthermore, the alloy should preferably notcontain more than 2 percent by weight iron since iron contents higherthan this are often detrimental to the finished casting.

The silicon-phosphorus alloy of this invention is seen to containcertain maximum allowable amounts of the SfifiZAlZ Patented May 1, 19%.?

elements phosphorus, aluminum, calcium, and iron. The limit set on thesematerials is made in view of the discovery that the disintegration ofsilicon-phosphorus alloys as currently produced was due to the chemicalunion of aluminum and/ or calcium impurities with phosphorus. Whenalloys are produced in accordance with this invention, wherein thestated materials are present only in the indicated amounts, the alloysproduced will be stable and nondisintegrating.

Aluminum and calcium are found in these siliconphosphorus alloys becausealuminum and calcium are contained in the silicon metal used inproducing the alloy. Iron contents result from the use offerrophosphorus to supply the phosphorus addition. By using siliconmetal having low aluminum and calcium contents, alloys can be producedwithin the indicated ranges.

It is believed that the actual mechanism of disintegration involves theformation of phosphides of aluminum and calcium in silicon-phosphorusalloys when these materials are present as impurities in certainamounts. These phosphides are extremely hygroscopic and, when exposed toa humid atmosphere, decompose to a white substance and evolve a gas thatis believed to be primarily phosphine. The decomposition reaction can bemicroscopically observed to result in the expansion of a unit areacontaining the phosphide. The pressures generated by this expansioncause the formation of cracks, and the eventual disintegration of thealloy.

Specific amounts of these materials are required before disintegrationtakes placer Aluminumis a very strong inducer of disintegration and soaluminum contents are always kept below 0.1 percent. Calcium alsoinduces disintegration and it has been found that the aggregate ofaluminum and calcium is preferably kept below 0.13 percent. Therefore,even if less than 0.1 percent aluminum is present, the calcium contentshould be low enough to keep the aggregate amount of aluminum andcalcium below 0.13 percent. The phosphorus content is preferably limitedto 1 percent and may be varied safely up to this amount provided thealuminum and calcium contents are kept below the indicated maximums.Phosphorus contents of 0.5 percent have been found adequate for mostfoundry uses.

It has also been found that the rate of cooling of these alloys affectsthe tendency to disintegrate. The slow cooled specimens have a greatertendency to disintegrate into powdery material than chilled or rapidlycooled specimens which tend to disintegrate into chunks with a lesseramount of powder. Specimens of heretofore produced silicon-phosphorusalloys, whether slow cooled or rapid cooled, still show objectionableamounts of disintegration, however.

Tests were conducted wherein the nondisintegrating nature of the alloysof this invention are shown in comparison to alloys in which aluminumcontents and calcium contents are not regulated. In Table I the resultsof studies made on several specimens of silicon-phosphorus alloyscontaining over 0.1 percent aluminum and some calcium are shown. Thebalance of the alloys is silicon. These alloys all disintegrated to agreater or lesser degree. Those alloys containing relatively largeaggregate amounts of aluminum and calcium, such as alloys 7 and 8,exhibit severe disintegration. It is also seen that the slow-cooledspecimens are more subject to disintegration than rapidly cooledspecimens.

TABLE I Dismtegratmg Alloys Percent Alloy No. Method of Amount of Disin-Cooling tegration P Ca Al 1 0.42 0.02 0.26 Chilledh'Ioderate-to-heavydisintegration to chunks. 2 0.42 0.02 0.26Slow-eeoled Moderate to fine disintegration to fine material. 3' 0.460.04 0.32 Chilled Heavy disintegration to chunks. 4'. 0.46 0.04 0.32Slow-cooled. l ioderate-to-heavydisintegration to fine material. 5; 0.40 0.004 0.26 Chilled Slight amount of disintegration to chunks. 6 0.400.004 0.26 Slow-cooled- Moderate-to-heavydisintegration to finematerial. 7 0.45 0.08 0.18 Chilled Heavy, 75% disiutegration to chunks.S 0.45 0.08 0.18 Slow-cooled Heavy, 90% disintegration to line material.

In Table II several specimens of alloys made according to this inventionare shown. These alloys were produced fromsilicon metal containing lowaluminum and calcium contents and ferrophosphorus containing 26 percentphosphorus metal. These alloys are prepared by melting the silicon andadding the ferrophosphorus. The iron-content of these alloys is notshown but was less thanZ percent and the balance is silicon. All ofthese alloys contain less than 0.1 percent aluminum and are able tocontain relatively large amounts of phosphorus without anydisintegration. The method of cooling does not afiec't the alloy. Slowcooled specimens do not disintegrate more severely than chilled alloysas did ordinary silicon-phosphorus alloys. However, a rapidly cooled orchilled alloy is preferable over a slow cooled material to minimize anypossibility of disintegration.

TABLE II N ondisintegrating- Alloys A'lloyNo. P Ca A1 Method of Amountof Cooling Disintegration 0.29 0. 01 0. 042 Chilled N o disintegration.0. 29 0. 01 0. 042 Slow-cooled Do. 0.51 0. 01 0. 042 Chilled Do. 0. 510. 01 0. 042 Slow-cooled. Do. 0. 60 0. 016 0. 028 Chilled D0. 0. 00 0.016 0. 028 Slow-coolecL Do. 0. 94 0. 01 0. 068 Chilled Do. 0. 94 0. 010. 068 Slow-cooled- Do. 0. 54 0. 04 0. 043 Chilled D0. 0. 54 0. 04 0.043 S1owcooled Do. 0. 59 0 04 0. 051 Chilled D0. 0. 59 0. 04 0. 051Slow-cooled- Do.

Several of these alloys were placed in a wet desiccator fordisintegration tests. Even after extended periods of time nodisintegration occurred as is the case when alloys having high aluminumcontents are similarly tested.

It is apparent, therefore, thatv these low-aluminum silicon-phosphorusalloys are suitable for foundry use, possessing great stability insevere transit and storage conditions, the alloys constitute a usefulcontribution to the metallurgical field.

The description of the invention above has been in terms of its specificembodiments. Modifications and equivalents will be apparent to thoseskilled in the art and this disclosure is intended to be illustrativeof, but not necessarily to constitute a limitation upon, the scope ofthe invention.

What is claimed is:

1. A nondisintegrating silicon-phosphorus alloy consisting essentiallyof from about 0.3 to '1 percent by weight phosphorus, less than 0.1percent by weight aluminum, and the balance substantially all siliconand incidental impurities.

2. A nondisintegrating silicon-phosphorus alloy consisting essentiallyof from about 0.3 to 1 percent by weight phosphorus, less than 0.1percent by weight aluminum, less than 0.13 percent by weight in theaggregate of calcium and aluminum Whencalcium is present in the alloy,less than 2 percentby Weight iron, and the balance substantially allsilicon and incidental impurities.

3. A nondisintegrating silicon-phosphorus alloy cohsisting essentiallyof about 0.5 percent by weight phosphorus, less thanill percentaluminum, less than 2 percent by weight iron, and the balancesubstantially all silicon andincidental impurities.

4. A nondisintegrating silicon-phosphorus alloy consisting essentiallyof about 0.5 percent by weight phosphorus, less than 0.1 percent byweight aluminum, less than 0.13 percent by "weight in the aggregate ofcalcium and aluminum when calcium is present in the alloy, less than 2percent by weight iron, and the balance substantially all silicon andincidental'impuritie's.

2,402,839 Ohl June-2s, 1946

1. A NONDISINTEGRATING SILICON-PHOSPHORUS ALLOY CONSISTING ESSENTIALLYOF FROM ABOUT 0.3 TO 1 PERCENT BY WEIGHT PHOSPHORUS, LESS THAN 0.1PERCENT BY WEIGHT ALUMINUM, AND THE BALANCE SUBSTANTIALLY ALL SILICONAND INCIDENTAL IMPURITIES.